1. Field
The present invention relates to a light emitting diode, and more particularly, to a gallium nitride based high efficiency light emitting diode in which a growth substrate has been removed by applying a substrate separation process.
2. Discussion of the Background
Since group III nitride such as a gallium nitride (GaN), an aluminum nitride (AlN), or the like, generally has excellent thermal stability and a direct transition type energy band structure, it has recently become prominent as a material for a light emitting element in visible ray and ultraviolet regions. Particularly, blue and green light emitting elements using indium gallium nitride (InGaN) have been utilized in various applications such as a large scale natural color flat panel display, a traffic light, indoor illumination, a high density light source, a high resolution output system, optical communication, and the like.
It is difficult to manufacture a homogenous substrate capable of growing a semiconductor layer of the group III nitride. Therefore, the semiconductor layer of the group III nitride is grown on a heterogeneous substrate having a similar crystal structure by a process such as a metal organic chemical vapor deposition (MOCVD) process, a molecular beam epitaxy (MBE) process, or the like. As the heterogeneous substrate, a sapphire substrate having a hexagonal structure is mainly used. However, sapphire is an electrical non-conductor, such that it limits a structure of a light emitting diode. Therefore, a technology of manufacturing a high efficiency light emitting diode having a vertical structure by growing epitaxial layers such as a nitride semiconductor layer on the heterogeneous substrate such as sapphire, bonding the epitaxial layers to a support substrate, and then separating the heterogeneous substrate using a laser lift-off technology, or the like, has been recently developed.
Generally, the vertical type light emitting diode has a structure in which a p side is positioned at a lower portion, such that current spreading performance is excellent as compared to a conventional lateral type light emitting diode. In addition, the vertical type light emitting diode uses a support substrate having thermal conductivity higher than that of sapphire, such that heat dissipating performance is excellent. Furthermore, a roughened surface is formed by anisotropically etching an N-surface by photo enhanced chemical (PEC) etching, or the like, thereby making it possible to significantly improve upward light extraction efficiency.
However, since the entire thickness (about 4 um) of the epitaxial layer is significantly thin as compared to a light emitting area of 350 um×350 um, or 1 mm2, there are many difficulties in current spreading. In order to solve this problem, a technology of promoting current spreading in an n-type layer by using an electrode extension extending from an n-type electrode pad or preventing current from directly flowing from a n-type electrode pad to a p-type electrode by disposing an insulating material at a position of the p-type electrode corresponding to that of the n-type electrode pad has been adopted. However, there is a limitation in preventing current flow from being concentrated from the n-type electrode pad thereunder. Furthermore, there is a limitation in uniformly spreading current over the entire wide light emitting region.